M.A. Rivadeneyra

Aerobic microbial dolomite at the nanometer scale: Implications for the geologic record

Microbial experiments are the only proven approach to produce experimental dolomite under Earths surface conditions. Although microbial metabolisms are known to induce dolomite precipitation by favoring dolomite growth kinetics, the involvement of microbes in the dolomite nucleation process is poorly understood. In particular, the nucleation of microbially mediated dolomite remains a matter for investigation because the metabolic diversity involved in this process has not been fully explored. Herein we demonstrate that Halomonas meridiana and Virgibacillus marismortui, two moderately halophilic aerobic bacteria, mediate primary precipitation of dolomite at low temperatures (25, 35 °C). This report emphasizes the biomineralogical implications for dolomite formation at the nanometer scale. We describe nucleation of dolomite on nanoglobules in intimate association with the bacterial cell surface. A combination of both laboratory culture experiments and natural samples reveals that these nanoglobule structures may be: (1) the initial step for dolomite nucleation, (2) preserved in the geologic record, and (3) used as microbial tracers through time and/or as a proxy for ancient microbial dolomite, as well as other carbonate minerals.

Biomineralization of carbonates by Halomonas eurihalina in solid and liquid media with different salinities : crystal formation sequence

Carbonate precipitation by 20 strains of the moderately halophilic species Halomonas eurihalina in both solid and liquid media was studied. The influence of salinity and temperature on the quantity and type of crystals precipitated was also investigated. Some strains of H. eurihalina formed crystals in all conditions tested. The mineral phases precipitated were magnesium calcite, aragonite and monohydrocalcite in variable proportions depending on various factors such as the type of growth medium employed and its salinity. Scanning electron microscopy and X-ray dispersive energy microanalysis were used to investigate the crystal formation sequence. The process of biolith formation was sequential. It started with chains or filaments of bacteria, giving way to discs which finally produced spherical forms of approximately 50 microns in diameter. We suggest a mechanism of carbonate crystal formation by H. eurihalina.

Biomineralization of carbonates by Halobacillus trueperi in solid and liquid media with different salinities.

We investigated the precipitation of carbonates by Halobacillus trueperi in both solid and liquid media at different salt concentrations and different magnesium/calcium ratios. H. trueperi precipitated at all assayed salt concentrations. When salt concentration increased, the quantity and the size of bioliths decreased and the time required increased. The precipitated minerals (determined by X-ray diffraction) were calcite, magnesium calcite and monohydrocalcite in variable proportions depending on the salinity and the physical state of the medium; the magnesium content of the magnesium calcites also varied with regard to the culture type. According to the saturation indices other minerals could also precipitate. Scanning electron microscopy showed that dominant morphologies of the bioliths were spherulitic with fibrous radiated interiors. We show that H. trueperi plays an active role in the precipitation of carbonates and we hypothesize about this process of biomineralization.

Carbonate and Phosphate Precipitation by Chromohalobacter marismortui

The ability of Chromohalobacter marismortui to precipitate carbonate and phosphate minerals has been demonstrated for the first time. Mineral precipitation in both solid and liquid media at different salts concentrations and different magnesium/calcium ratios occurred whereas crystal formation was not observed in the control. The precipitated minerals were studied by X-ray diffraction, scanning electron microscopy and EDX, and were different in liquid and solid media. In liquid media aragonite, struvite, vaterite and monohydrocalcite were precipitated forming crystals and bioliths. Bioliths accreted preferentially close to organic pellicles, whereas struvite preferentially grows in microenvironments free of such pellicles. Magnesian calcite, calcian-magnesian kutnahorite, “proto-dolomite” and huntite were formed in solid media. The Mg content of the magnesian calcite and of Ca-Mg kutnahorite also varied depending on the salt concentration of the culture media. This is the first report on bacterial precipitation of Ca-Mg kutnahorite and huntite in laboratory cultures. The results of this research show the active role played by C. marismortui in mineral precipitation, and allow us to compare them with those obtained previously using other taxonomic groups of moderately halophilic bacteria.

Precipitation of carbonates by Bacillus sp. isolated from saline soils

We studied carbonate precipitation by 26 moderately halophilic strains of Bacillus isolated from a saline soil, haplic Solonchac. They were cultured in both solid and liquid media with salt concentrations varying between 2.5% and 20% (w/v). Bacillus sp. formed mineral crystals in all the media tested, although the mineral precipitation diminished as salinity increased. The minerals that were precipitated included magnesium calcite, aragonite, monohydrocalcite, and dolomite, in varying proportions depending upon the growth medium used. We studied the morphology of the bioliths by means of scanning electron microscopy. We compared our results with those obtained using other taxonomic groups of moderately halophilic bacteria. We discuss possible mechanisms for formation of these biominerals and the probability of their formation in natural habitats.

Precipitation of calcium carbonate byDeleya halophila in media containing NaCl as sole salt

The precipitation of calcium carbonate by 27 strains ofDeleya halophila using solid and liquid media containing different NaCl concentrations (2.5, 7.5, or 20%, wt/vol) as sole salt, and two incubation temperatures (22° and 32°C) have been studied. All the strains tested were able to precipitate calcium carbonate under the different environmental conditions assayed. Crystals formed were calcite and vaterite; the ratio of calcite to vaterite was dependent on total salts and on the type of medium.

Process of Carbonate Precipitation by Deleya halophila

Abstract. Scanning electron microscopy and X-ray dispersive energy microanalysis were used to investigate the formation of carbonate crystals by Deleya halophila. The formation of calcium carbonate crystals (polymorphous aragonite) by D. halophila is a sequential process that commences with a nucleus formed by the aggregation of a few calcified bacterial cells and the subsequent accumulation of more calcified cells and carbonate, which acts to weld the bacteria together. The process leads to the formation of spherical bioliths measuring approximately 50 μm in diameter. The mechanism of carbonate precipitation by D. halophila under our working conditions represents a process of induced biomineralization.

Calcium carbonate formation by Deleya halophila: Effect of salt concentration and incubation temperature

Abstract The precipitation of calcium carbonate by strains of the moderately halophilic species Deleya halophila was studied. The influence of salinity and temperature on the formation and type of crystals formed by these strains was also investigated. All strains tested were capable of precipitating CaCo3. Low temperature and high salinity were negative factors affecting crystal formation. Calcite (with variable Mg2+ content) was the only crystal formed under all conditions tested. Aragonite was not detected even at high Mg2+ concentration in the medium.

Bacterial formation of struvite

We studied the formation of exocellular precipitates of struvite (Mg NH4PO4.6H2O) by 96 kinds of calcite‐pro‐ducing bacterial strains isolated from soil. We also studied the influence of calcium ions on struvite precipitation. The number of strains producing struvite was 20. Only four consistently formed large amounts. These results seem to indicate that the bacterial precipitation of struvite is not a general phenomenon. The strains studied were taxonomically identified, and no relationship was found between the production of struvite and the taxonomic identity of such strains. Calcium, supplied as Ca acetate in the culture medium, appeared to inhibit the biological precipitation of struvite.

Precipitation of carbonates by Nesterenkonia halobia in liquid media.

We investigated the precipitation of carbonates by Nesterenkonia halobia in a liquid medium at different concentrations of salts and incubation times. N. halobia only produced crystals at salt concentrations of 2.5%, 7.5% and 15%. At 20% salt concentration no crystal formation was observed. Calcite, aragonite and dolomite were precipitated in different quantities, depending on the salinity of the medium and incubation time. Scanning and transmission electron microscopy, microanalysis and electron diffraction were all used to study in detail the morphology, composition and internal structure of the bioliths. We propose a mechanism for biolith formation involving both biological and inorganic processes.